"The Government of the United States of America has rights in this invention pursuant to Contract No. DE-AC21-93-MC30246 awarded by the U.S. Department of Energy."
High performance gas turbine engines require cooling passages and cooling flows to ensure reliability and cycle life of individual components within the engine. For example, to improve fuel economy characteristics, engines are being operated at higher temperatures than the material physical property limits of which the engine components are constructed. These higher temperatures, if not compensated for, erode engine components and decrease component life. Cooling passages are used to direct a flow of coolant, such as air, to such engine components to reduce the high temperature of the components and prolong component life by limiting the temperature to a level which is consistent with material properties of such components.
Conventionally, a portion of the compressed air is bled from the engine compressor section to cool these components. Thus, the amount of air bled from the compressor section is usually limited to insure that the main portion of the air remains for engine combustion to perform useful work.
As the operating temperatures of engines are increased, to increase efficiency and power, either more cooling of critical components or better utilization of the cooling air is required.
Various arrangements for using cooling air to increase cycle life and reliability are available. U.S. Pat. No. 4,292,008 issued to William C. Grosjean et al on Sep. 29, 1981 discloses a cooling flow system. The system includes an air cooled turbine blade in which cooling air enters from a cavity through a passage to the root of the internally cooled rotor blades. A part of the cooling air is delivered through a longitudinally extending uniform passage in the disc intermediate the root of the blade and the disc. The narrow constant cross-section area of the space between the fir tree passage in the disc and the blade root is small and uniform and provides an extremely high local convective heat transfer coefficient through the passage. A uniform passage resulted in an increase in heat transfer associated with the high level of turbulence at the inlet but did not provide a uniform disc ring temperature along the axial length of the disc.
Another arrangement for using cooling air to increase cycle life and reliability is disclosed in U.S. Pat. No. 4,668,162 issued to Philip J. Cederwall et al on May 26, 1987. In this patent a cooling system includes a nozzle and shroud assembly having a plurality of through passages for transferring cooling air through the nozzle and a separate passage providing nozzle inner shroud cooling. From a reservoir below the nozzle a plurality of passages are provided for the cooling air to exit into an area below the turbine blades for buffering the hot main stream gas from reaching the rotor.